The existing 3G (3rd-generation mobile communication technology)/4G (4th-generation mobile communication technology) FDD (Frequency Division Duplexing) mobile terminals adopt a full duplex design, so the transmitting path and the receiving path thereof operate simultaneously. In the conventional FDD radio frequency (RF) architecture, the duplexer is an essential device, which mainly functions to:
1) combine the transmitting path and the receiving path together; and
2) perform filtering on the transmitting path and the receiving path.
The conventional duplexes have a relatively large insertion loss (IL); and especially in the case that the frequency is high and the transmitting frequency band is close to the receiving frequency band, the insertion loss is very large. For example, the duplexer used in WCDMA BC2 (Wideband Code Division Multiple Access BC2) has an insertion loss of above 2.5 dB because the transmitting frequency band is 1850 MHz-1910 MHz and the receiving frequency band is 1930 MHz-1990 MHz. This requires use of a band-pass filter (BPF) having a central frequency of 1950 MHz and a transition frequency band of only 20 MHz, which is very difficult to be implemented.
Such a great insertion loss leads to the following problems:
1) the problem of large power consumption. Because of the large insertion loss, the output power of the amplifier must be increased to ensure an adequate output power, and this will necessarily increase the power consumption.
2) the problem of heat dissipation. The increased output power and the increased power consumption will necessarily lead to generation of more heat. Heat generation of power amplifiers of the conventional WCDMA terminals is considerable, which has an influence on the battery and the user experience.
3) The problem of cost. Devices of high technical specifications necessarily have high cost.
Referring to FIG. 1, an RF framework of a typical WCDMA+GSM dual-mode terminal is shown therein. The WCDMA+GSM dual-mode terminal mainly comprises an antenna 95, a duplexer 90, a wireless transceiver 10, a plurality of signal receiving branches and a plurality of signal transmitting branches.
As two signal receiving branches, a GSM980/850 RX SAW module 20 and a DCS/PCS RX SAW module 30 are configured to receive an RF signal obtained by the antenna 95 and gated by the duplexer 90. The wireless transceiver 10 obtains the RF signal, which has been processed by the GSM980/850 RX SAW module 20, via a port 1011 and a port 1012, and obtains the RF signal, which has been processed by the DCS/PCS RX SAW module 30, via a port 1013 and a port 1014.
A GSM HB PA (GSM High Band Power Amplifier) 40 and an HB MN (High Band Match Network) 41 constitute a GSM signal transmitting branch. The wireless transceiver 10 transmits a GSM high band (HB) signal via a port 1015 to the GSM HB PA 40 and the HB MN 41. The GSM HB PA 40 and the HB MN 41 perform power amplifying and network matching respectively on the GSM HB signal. The GSM HB signal which has been processed is transmitted by the antenna 95 after being gated by the duplexer 90.
A GSM LB PA (GSM Low Band Power Amplifier) 50 and an LB MN (Low Band Match Network) 51 constitute another GSM signal transmitting branch. The wireless transceiver 10 transmits a GSM low band (LB) signal via a port 1016 to the GSM LB PA 50 and the LB MN 51. The GSM LB PA 50 and the LB MN 51 perform power amplifying and network matching respectively on the GSM LB signal. The GSM LB signal which has been processed is transmitted by the antenna 95 after being gated by the duplexer 90.
A WCDMA BC1 PA (WCDMA BC1 Power Amplifier) 60, a W MN1 (WCDMA Match Network) 61, a duplexer 62 and a DPX MN (Duplexer Match Network) 63 constitute a WCDMA signal transmitting/receiving branch, which is configured to transmit or receive a WCDMA BC1 signal. The wireless transceiver 10 transmits a BC1 signal via a port 1019. The WCDMA BC1 PA 60, the W MN1 61 and the DPX MN 63 perform power amplifying and network matching respectively on the BC1 signal. The BC1 signal which has been processed is transmitted by the antenna 95 after being gated by the duplexer 90. The duplexer 62 can be used to select a path that allows the BC1 signal transmitted by the wireless transceiver 10 via the port 1019 to be transmitted via the antenna 95 or allows the wireless transceiver 10 to obtain a corresponding WCDMA signal from the antenna 95 via a port 1017.
Likewise, the wireless transceiver 10 generates a WCDMA BC2 signal and a WCDMA BC5 signal respectively via ports 1022 and 1023 and, via ports 1017 and 1018, obtains a BC2 signal and a BC5 signal received by the antenna 95 from the outside respectively. Thus, the ports 1022 and 1023 respectively correspond to two WCDMA signal transmitting branches, and the ports 1017 and 1018 respectively correspond to two WCDMA signal receiving branches. The architecture of the aforesaid WCDMA signal transmitting/receiving branch is completely the same as that of the aforesaid WCDMA signal transmitting/receiving branch corresponding to the BC1 signal, and thus will not be further described herein.
Additionally, an RF connector 92 and an ANT MN (Antenna Match Network) 94 are further provided between the antenna and the duplexer 90. The RF connector 92 and the ANT MN 94 are respectively configured to couple a plurality of signals from different signal sources into one signal and perform antenna matching on the signal.
In conventional mobile communication terminals, the duplexer 90 mainly functions to:
1) combine the transmitting path and the receiving path together; and
2) providing an isolation between the transmitting path and the receiving path, that is, attenuating the noise caused by the RF signal in the transmitting path within the receiving frequency band, thereby protecting receiving signals from the interference caused by the RF signal.
The reason for the need of providing an isolation between the transmitting path and the receiving path is that, the receiving path requires a high sensitivity (which is typically −110 dBm in conventional technologies), while the transmitting path is a high-power path, the intensity of which can be up to 28 dBm. Because of the non-linearity of the RF system, there necessarily exists very intensive out-of-band (OOB) strays in the case that the main wave is 28 dBm. Such strays will be directly fed to the receiving end if they are not isolated at the receiving frequency band, and the intensity thereof will be higher than that of the useful receiving signals. Finally, the receiving performance is influenced.
The receiving system design for WCDMA signals of the mobile communication terminal shown in FIG. 1 is analyzed as follows:
The typical receiving sensitivity of a conventional WCDAMA terminal is −110 dBm.
The power of the DPDCH (Dedicated Physical Data Channel) is −120.3 dBm.
The channel code rate for WCDMA sensitivity test is 12.2 kbps, and the code gain is 10×log (3.84 MHZ/12.2)=25 dB.
The decoding threshold for QPSK modulation of the WCDAMA is 5.2 dB, and a margin of 2 dB needs to be reserved, so an input signal to noise ratio (SNR) of 7.2 dB is required for the demodulation module.
Therefore, the noise at the input end of the demodulation module should be below:−120.3+25−7.2=−102.5 dBm/3.84 MHz=−168.343 dBm/Hz.
Taking a typical noise figure of 5 dB of the wireless transceiver 10 into consideration, the noise at the input end of the demodulation module is required to be below −173.343 dBm/Hz.
The system thermal noise is:KBT=−200+26.022=−173.977 dBm/Hz=−108.13 dBm/3.84 MHz
where K (Boltzmann constant)=1.38×10−20 mJ/K, B=3.84 MHz (65.843 dB), T=290 K.
The typical output noise of the power amplifiers (60, 70 and 80) is:−160 dBm/Hz (the output of the wireless transceiver)+28 dB (the typical amplifier gain of the amplifier at the receiving frequency band)=−132 dBm/Hz=−66.16 dBm/3.84 MHz.
Therefore, the duplexer 90 is required to provide an isolation of at least 173.343−132=41 dB.
With such a great isolation, the insertion loss of the conventional duplexers is relatively large.
Accordingly, an urgent need exists in the art to provide an antenna modulation method for a mobile communication terminal capable of solving the aforesaid problems.